It’s great that embedded videos are now responsive.
However there is a slight issue. When seen on a smaller screen/resized to small - the video itself is responsive and goes smaller as the window is made smaller, but the player frame does not respond in the same way.
When you look at an embedded video the player frame is a vertical rectangle, rather than horizontal. (I use iframe, so not sure if this happens when using URL)
The same result for YouTube and Vimeo videos.
I’ve tested this in Firefox browser and the iPhone.